Flow regulators with small, precision orifices are employed in numerous industrial applications, including, for example, fuel injectors in internal combustion automotive engines and rocket engines, thermal ink jet printheads, and in similar services requiring the precise metering of a fluid.
Conventional methods for fabricating flow regulators include casting from a mold, machining, and electroplating. Further, these methods may require a finishing step to produce the final product.
Electroplating methods for fabricating flow regulators employ various combinations of dry and liquid resists, and etching. Such methods are limited, however, in that the maximum electroformed layer thickness achievable is approximately 200 microns.
Prior art methods of fabricating flow regulators have generally suffered from a lack of precision in orifice generation. Until now, such methods have comprised joining discrete components to form flow regulators.
For example, William P. Richardson, Michigan Technological University Master's Thesis: "The Influence of Upstream Flow Conditions on the Atomizing Performance of a Low Pressure Fuel Injector" (1991), discloses nozzles produced by a process of Silicon MicroMachining (SMM). In this process, orifice configuration is provided by silicon etching.
U.S. Pat. No. 4,586,226 to Fakler et al. relates to a method of fabricating a small orifice fuel injector using a wax and silver technique, followed by post-finishing. A first layer of Ni is electrodeposited on a stainless steel base plate, in which fuel feed passages are formed. Connecting bores to the perforations are made through a face plate Ni layer. Plastic mandrels are fabricated having legs with support sections, orifice forming sections and coupling tabs for tying the legs together. The support sections of the mandrels are set into acceptor holes formed in the face plate and a bonded layer of rigid material is built up by electrodeposition to enclose the orifice forming sections. The sections of the mandrels extending outside the bonded layer are removed and the surface is smoothly finished.
U.S. Pat. No. 4,246,076 to Gardner relates to a multilayer dry film plating method for fabricating nozzles for ink jet printers. The process comprises the steps of coating a first layer of a photopolymerizable material on a substrate, and exposing the layer to a pattern of radiation until at least a portion of the layer of photo-polymerizable material polymerizes. A free surface of the first layer is coated with a second layer of a photopolymerizable material, the process being analogous to the process associated with the deposition of the first layer. Both the layers are developed to remove non-polymerized material from the substrate followed by metallic deposition on the substrate by electroplating.
U.S. Pat. No. 4,229,265 to Kenworthy discloses a thick dry film resist plating technique for fabricating an orifice plate for a jet drop recorder. A sheet of stainless steel is coated on both sides with a photoresist material. The photoresist is then exposed through suitable masks and developed to form cylindrical photoresist peg areas on both sides of the sheet. Nickel is then plated on the sheet until the height thereof covers the peg edges. A larger diameter photoresist plug is then formed over each photoresist peg. Nickel plating is then continued until the height is level with the plug. The photoresist and plate are then dissolved and peeled from the nickel forming two solid homogeneous orifice plates.
U.S. Pat. No. 4,675,083 to Bearss et al. relates to a method of manufacturing metal nozzle plates associated with an ink jet printhead by using a two-step resist and plating process. The method comprises the steps of providing a first mask on a metal substrate that includes a first plurality of mask segments and providing a second mask including a second plurality of segments formed atop the first plurality of segments. This structure is then transferred to an electroforming station wherein a layer of nickel is formed on exposed surfaces up to a thickness of about 2.5 mils. Once the plate is completed to a desired thickness, negative and positive photoresist mask segments are removed using conventional photoresist liftoff processes.
U.S. Pat. No. 4,954,225 to Bakewell relates to a method for electroforming nozzle plates having three-dimensional features. The method employs a dry film over liquid, and a thick film photoresist. A conductive coating is applied to a surface of a transparent mandrel using photolithographic techniques. A pattern of thin, circular masked areas of a non-conductive, transparent material is formed over each hole formed in the opaque, conductive coating. A layer of first metal is plated onto the conductive coating on the transparent mandrel. A layer of second metal is plated over the first metal layer until the first layer of the second metal surrounds, but does not cover, the photoresist posts. Depressions caused in the metal layers are filled with fillers to create smooth continuous surface on the top of the plate layers. A thick layer of photoresist is then applied over the top of the smooth plated layers and cured so as to form a pattern of thick photoresist discs covering and in registration with the filled depressions. The plated layers are then separated from the transparent mandrel and the extraneous material is stripped using suitable stripping techniques.
U.S. Pat. No. 4,839,001 to Bakewell relates to a method of fabrication of an orifice plate using a thick film photoresist in which the plate is constructed from two electroformed layers of nickel. A first layer of Ni is electroformed onto a conductive mandrel to form a support layer with a selected hole pattern. Copper is plated over the Ni to cover the holes. A second layer of Ni is electroformed onto the surface that is joined to the mandrel in such a way as to form an orifice layer with a pattern of smaller holes of selected cross section in alignment with the pattern of holes of the first nickel layer. The copper is then etched away to reveal a thin orifice plate of Ni.
U.S. Pat. No. 4,716,423 to Chanet al. relates to a process employing the application of a first liquid and then a dry film for the manufacture of an integrated orifice plate. The process consists of forming a first mask portion having a convergently contoured external surface and a second mask portion having straight vertical walls. A first metal layer is electroformed around the first mask portion to define an orifice plate layer and electroforming of the second metal layer is done around the second mask portion to define a barrier layer of discontinuous and scalloped wall portions having one or more ink reservoir cavities. Finally, the first and second masks, and selected portions of metallic substrate, are removed, thereby leaving intact the first and second metal layers in a composite configuration.
U.S. Pat. No. 4,902,386 to Herbert et al. relates to a cylindrical electroforming mandrel and a thick film photoresist method for fabricating and using the same.
U.S. Pat. No. 5,167,776 to Bhaskar et al. discloses an orifice or nozzle plate for an ink jet printer that may be produced by a process comprising providing electroplating over the conductive regions and over a portion of the insulating regions of a mandrel to form a first electroformed layer having convergent orifice openings corresponding to the insulating regions. The electroplating process may be repeated once to form a second electroformed layer on the first electroformed layer, said second layer having convergent orifice openings aligned with those of the first layer.
U.S. Pat. No. 4,972,204 to Sexton discloses an orifice plate for an ink jet printer produced by a multilayer electroforming process comprising the steps of forming resist pegs on a substrate and electroplating onto said substrate a first metal layer complementary to said resist pegs, allowing the metal to slightly overgrow the top surface of the resist pegs and form a first electroformed layer. A first resist layer in the form of a channel wider than the resist pegs is placed on the resist pegs and the first electroformed layer. A second electroformed layer is formed around the first resist layer and on the first electroformed layer. A series of resist layers of ever-increasing width and electroformed layers of ever-decreasing width are subsequently layered onto the nascent orifice plate in like fashion to eventually form an orifice plate having orifices opening into a channel that progressively widens upstream from the orifices.
Copending U.S. application Ser. No. 08/371,118, filed Jan. 11, 1995, discloses multilayered fluid dispersant spray directors incorporating structure producing upstream turbulence generation, and multilayer resist processes for producing such spray directors.
Prior art fluid regulators have been known to suffer from the drawbacks of downstream "dead space" or "sack volume" during periods of inactivity. When fluid flow through such flow regulators is stopped, residual fluid remains within the cavities of the flow regulators. This residual fluid may leak from the flow regulators at inopportune times, thus causing various problems. For example, prior art engine fuel injectors have suffered from residual fuel leakage during the non-injecting part of the engine cycle, leading to, e.g., diminished efficiency and increased emission of hydrocarbon pollutants.
Another problem known to be related to residual fluid being retained in the dead space of prior art flow regulators having non-zero sack volume has been the tendency of certain residual fluids to clog the flow regulators when retained within the dead space for a sufficient amount of time to coagulate.
The above references are incorporated herein by reference in their entireties.